The juvenile hormone binding compounds with high affinity for this ligand have been identified in cytosol of fat bodies from adults of Leucophaea. For further characterization of each of these compounds, purification by ion exchange chromatography, sucrose density gradient centrifugation and isoelectrofocusing in essential. A comparison of the characterized compounds is made with the hemolymph JH carrier, since this compound is presumably produced in the fat bodies as well as thus constitutes a contamination of the JH receptor preparations. The potential role of the JH carrier in the uptake of JH by the target tissue is to be studied as well. The ontogeny of the very high affinity cytosol receptor during metamorphosis will be investigated. The binding characteristics of the JH analog ZR-515, a compound which induces vitellogenin synthesis, to cytosol and nuclear binding compounds has to be studied. Furthermore, an attempt will be made to identify the hormone binding characteristics to chromatin from target and non-target tissues. The sum of the information gathered in the various projects will identify the mode of JH action in the target tissue and will broaden the concept of receptor mediated hormone action to the sesquiterpenoid insect juvenile hormone.